A material having a widthwise modified cross-section along its length is used for a transistor lead frame and a connector. As for a method of manufacturing the modified cross-section material, a cutting method, a machining method using a V-type dice and a roll, and a rolling method are known.
In a conventional method of manufacturing a modified cross-section material such as the rolling method, a material is inserted between a grooved roll having a groove in the center thereof and a flat roll. Then, the material is inserted between two flat rolls. Thus, modified cross-section material having two thin parts on the both sides thereof and a thick part in the center thereof is formed.
Next, the modified cross-section material is inserted between a grooved roll having a smaller groove than that of the prior grooved roll and a flat roll. Then, the material is inserted between two flat rolls. Thus, the modified cross-section material having wider thin parts than the prior thin parts is formed.
As the above, the modified cross-section material with a predetermined form is manufactured by the repetition of rolling with a grooved roll having a smaller groove than the prior and a flat roll.
In general, when the modified cross-section material is manufactured from a flat board material, there is a difference between an elongation of the center part and that of the side parts. A waveform and/or a torsion occur in the manufactured material by the difference between the elongations. As a solution of these, in the Japanese Patent Kokai No.59-78701, it is disclosed that the both side parts of the material are rolled, without rolling the center part of the material, by using the grooved roll and the flat roll, then, the modification of the both side parts occurs both in the groove of the grooved roll and between both sides of the grooved roll and the flat roll in the widthwise direction, thus, the elongations of the both side parts are balanced with the elongation of the center part.
Another method of manufacturing a modified cross-section material is disclosed in the Japanese Patent Kokai No.61-50064.In this conventional method of manufacturing a modified cross-section material, a material is inserted between a first convex roll having two convex parts and a flat roll. Then, the material is inserted between a second convex roll and a flat roll. One side face of the convex part is a slant face. The convex part of the first convex roll is smaller than that of the second convex roll. Namely, the convex part of a next convex roll is bigger than that of a prior convex roll.
As the above, the modified cross-section material with a predetermined form is manufactured by the repetition of rolling with a convex roll having two bigger convex parts than the prior convex parts and a flat roll.
A further conventional method of manufacturing a modified cross-section material is disclosed in the Japanese Patent Kokai No.1-133603. In this conventional method, the modified cross-section material is manufactured by the repetition of rolling with rolls based on a predetermined modification factor and annealing. Thus, the size accuracy of the modified cross-section material is improved.
Among the conventional methods of manufacturing a modified cross-section material, however, the cutting method has disadvantages in that the manufacturing cost is high, because a great loss of material is caused by cutting scraps. On the other hand, the machining method using a V-type dice and a roll has disadvantages in that the machining speed can not be high and it is difficult to improve in the productivity, because the machining process is to be interrupted due to the pressure caused by reciprocating motion of the rolls.
Further, the rolling method has disadvantages in that the rough surface is occurred in the thick part, because the thick part is not rolled in the groove of the grooved roll, and the quality of the manufactured material is to be poor due to the inequality of the thick part because the sides of the thick part are thicker than the center of that due to the inflow of material into the groove of the grooved roll.
Even further, the method in the Japanese Patent Kokai No.61-50064 has disadvantages in that the rough surface and the inequality of the thick part are occurred by the same reason as the above, and the width of the thin part which is formed by one rolling phase is smaller than that of the rolling method, because the modification of the material is occurred generally in only the both side parts (i.e. the thin parts).
Further, the methods in the Japanese Patent Kokai No.59-78701 and No.61-50064 have disadvantages in that the difference between the modification quantity of the rolled thin parts and the unrolled thick part is occurred along its length on the material, because it is difficult that the modification of the rolled part is perfectly occurred on the material in the widthwise direction, and though the difference between the modification quantities of the rolled thin parts and the unrolled thick part is different, according to the form of the roll and the modification extent, a waveform-deformation and/or a torsion occur in the manufactured material, when the difference is large.
Even further, the Japanese Patent Kokai No.1-133603 has disadvantages in that the operability and the productivity in manufacturing the modified cross-section material are poor, because the manufacturing process is not completed at one process (rolling phase).